Commercial aircraft typically include environmental control systems that regulate air supply, temperature, and cabin pressurization on the aircraft. Such environmental control systems may also be utilized to provide cooling to components of the aircraft itself, such as electrical systems. The environmental control system of most jet aircraft typically includes two or more air cycle machine cooling devices, which provide pressurized air of an appropriate temperature to the cabin of the aircraft by utilizing heated, pressurized bleed air from the jet engines or auxiliary power unit of the aircraft, as well as ram air, which is ambient air that enters the aircraft through a ram scoop.
A typical air cycle machine includes a turbine that is mechanically connected to a compressor, such that the turbine provides a rotational force to the compressor in order to operate the compressor. The turbine and compressor are selectively operable and cooperate to reduce the temperature of the bleed air to allow cooling of the aircraft. However, a typical air cycle machine also includes a heat exchanger that cools the bleed air using the ram air. When the aircraft is in flight, the ambient air temperature is so low that operation of the turbine and compressor is not needed to cool the bleed air, and thus, the turbine and compressor air typically only operate when the aircraft is flying at low altitude or on the ground.
While the air cycle machines are well-suited to conditioning and pressurizing air both while the airplane is on the ground and while the airplane is in flight, the air cycle machines are heavy, and the added weight that must be carried by the aircraft causes an increase in fuel consumption. Furthermore, in applications where passengers are not being transported by the aircraft, the presence of redundant air cycle machines on the aircraft is unnecessary, and simultaneous operation of these redundant systems further increases fuel consumption. Accordingly, it would be desirable to have an environmental control system for an aircraft that was of reduced weight and complexity.